Abolish speed limits universally. No need to look at the dash at all then. Save a fortune in hardware and police too, so that they can get on with catching criminals. Yes, I hear you safety campainers - people killed and all that jazz, but do we really need the nanny state telling us not to kill ourselves? Control speed with road humps, pedestrian safety barriers and chicanes in urban areas and forget it out in the country or the motorways where pedestrians are limited and shouldn't be wandering around like dopey bozos. No need for HUD or anything then, other than a light to tell you when to top up with fuel.